The natural history, survival duration, and response to therapy in breast cancer is very diverse, even within specific staging subgroups. Clinical factors, to a certain extent, have provided information regarding prognosis; however, biological factors which might enlighten us regarding mechanisms of progression are sorely lacking. Based on the observation of hematologic malignancies and preliminary results involving solid tumors including breast cancer, we predict that cytogenetic analysis should provide significant information regarding natural history and survival. The studies proposed will correlate chromosomal alterations with certain clinical and biological features of this disease and compare these changes with known prognostic factors. A. SPECIFIC AIMS 1. To investigate karyotypic abnormalities in primary breast cancer and determine if there are consistent clonal changes which may relate to